1,721,053 research outputs found
Absorption and saturation mechanisms in aluminium laser ablated plasmas
No full textWe have measured time-of-flight (TOF) distributions of positive ions in plasmas produced by laser ablation of Al targets at the second (lambda = 532 nm) and third (lambda = 355 nm) harmonic of Nd:YAG laser radiation. The investigation has been carried out in a regime of relatively high laser fluences (1-60 Jcm(-2)). The interpretation of the ion TOF distributions in terms of theoretical shifted Maxwell-Boltzmann distributions produces a good agreement with the experimental data. This has allowed us to infer the ion flow velocity and temperature associated with the measured TOF distributions, as well as the ion kinetic energies as a function of the laser fluence. We have also studied the total ion yield at different laser fluences. Our results show that all the plume parameters investigated are increasing functions of the laser fluence until a saturation plateau is reached at high fluences (> 20 Jcm(-2)). We ascribe this saturation behaviour to strong absorption and partial, or total, reflection of the laser light by the hot plasma produced by the leading edge of the intense laser pulse. This interpretation is supported by a semi-quantitative analysis of the laser photon absorption and ionization mechanisms in Al plasma, at both laser wavelengths
Power consumption in stirred tanks provided with multiple pitched-blade turbines
No full textThe power consumed by one, two, or three downward pumping, 45 degrees six-blade pitched-blade turbines (6-PBTs) mounted on the same shaft was experimentally determined in stirred tanks under turbulent conditions. The power drawn by each individual impeller (in single- or multiple-impeller configurations), as well as the total power consumption, was measured with strain gauges mounted on the shaft and reported as individual or total power numbers. The power dissipated by single downward pumping, 45 degrees four-blade pitched-blade turbines (4-PBTs) was also determined. Different combinations of the number of impellers, impeller diameter-to-tank diameter ratio, off-bottom clearance of the lowest impeller, C-bl, and spacing among impellers were tested. The overall power numbers of double 6-PBT systems were typically found to be smaller than twice the power number of a single 6-PBT. When C-bl was low and the upper impeller distant from the lower impeller, the power number of the lower impeller and the overall power number were higher. Reducing the distance between the impellers lowered the overall power number and that of the lower impeller. Similar results were obtained with three 6-PBTs. The results of this work can be used to predict the power consumed by individual impellers in multiple 6-PBT systems in a turbulent flow regime and to determine the optimal impeller configurations to minimize energy consumption
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